text: 
  #ifndef EX_H
  #define EX_H
  
  struct Ex{
  	string ex;		//what happened
  	int pos;		//source offset
  	string file;
  	Ex( const string &ex ):ex(ex),pos(-1){}
  	Ex( const string &ex,int pos,const string &t ):ex(ex),pos(pos),file(t){}
  };
  
  #endif